Renewable fuse



March 16, 1937. c, J MCHUGH 2,@74,06@

RENEWABLE FUSE Original Filed Sept. 13, 1934 2 Sheets-Sheet l IN VENTOR.

' Z3 GJNHUgH. ZZZZfl/Z ATTORNEY;

March 16, 1937. c. J. MCHUGH 2,074,060

RENEWABLE FUSE Original Filed Sept. 13, 1934 2 Sheets-Sheet 2 INVENTOR' C J McHU H.

Patented Mar. 16, 1937 RENEWABLE FUSE Charles J. McHugh, Indianapolis, Ind., assignor, by mesne assignments, to George M. Rich Refiled for abandoned application Serial No. 743,853, September 13, 1934. This application August 19, 1936, Serial No. 96,840

10 Claims.

This invention appertains to fuse of the type employed in electric line circuits for protection against overload, short circuits, etc.

One of the salient objects of my invention is to provide an electric fuse which can be conveniently and quickly re-set after the same has blown, whereby the fuse can be used over and over again.

Another important object of my invention is to provide an electric fuse having a pair of spaced contacts therein adapted to be normally connected by a liquid conductor, such as mercury, which is adapted to blow to break the circuit when the current reaches a predetermined amperage, the mercury being returnable between the contacts for closing the circuit by proper manipulation of the fuse.

A further object of my invention is the provision of a capillary bore between the contacts for the mercury and an expansion chamber beyond the bore, the mercury being adapted to blow into the expansion chamber from the bore and return into the bore upon the condensation of the mercury and the shaking of the fuse.

A further important object of my invention is the provision of a small reservoir chamber between the contacts and the expansion chamber having restricted outlets, whereby the mercury column will be maintained in the bore between to the contacts irrespective of the position of the fuse. I

A further object of my invention is the provision of a contact (such as copper) at the opposite ends of the bore having an affinity for mercury, whereby to facilitate the making of the circuit between the contacts and the maintaining of the circuit irrespective of the position of the fuse.

A further object of my invention is to provide means for regulating the blowing of the fuse by different current values according to the diameter and length of the capillary bore, whereby fuses can be manufactured and sold for all different purposes.

A further object of my invention is the provision of novel means for incorporating a safety fuse link in the fuse body and in circuit with the contacts and the mercury column, adapted to blow at a greater amperage than the mercury column, so that if the bore becomes enlarged by repeated blowings of the mercury column and thus carry a greater current value than that for which the fuse was designed, the safety link will blow and thus protect the circuit.

" A further object of my invention is the provi- Cal sion of a slidable indicator plunger disposed in the expansion chamber, whereby upon the blowing of the fuse such indicator plunger will be forced to the outer end of the chamber beneath a sight window, so that the same can be readily seen by an observer and thus permit the easy finding of a blown fuse.

A further object of my invention is the provision of a novel cartridge adapted to be incorporated in the body of a fuse provided with the necessary contacts, the capillary bore, reservoir and expansion chamber, whereby to facilitate the economical manufacture of the fuse.

A further object of my invention is the provision of a substantially air-tight cartridge. whereby upon the blowing of the fuse a sumcient pressure will be created to dampen or smother the are which might take place between the contacts.

A still further object of my invention is to provide an improved renewable fuse of the above character, which will be durable and eflicient in use, one that will be simple and easy to manufacture, and one which can be placed upon the market at a reasonable cost.

With these and other objects in view, the invention consists in the novel construction, arrangement and formation of parts, as will be hereinafter more specifically described, claimed, and illustrated in the accompanying drawings, in which drawings:

Figure 1 is an enlarged longitudinal section through a fuse plug constructed in accordance with my invention, the plug being shown in an upright position ready for use.

Figure 2 is an enlarged fragmentary longitudinal section showing the plug in a horizontal position ready for use.

Figure 3 is a view similar to Figures 1 and 2, but showing the plug in a reversed position from Figure 1.

Figure 4 is a view similar to Figure 2 showing the plug at the time of the blowing thereof, with the indicator plunger forced to the outer end of the expansion chamber to its indicating position.

Figure 5 is a fragmentary end elevation of the fuse plug with the indicator plunger in its indicating position.

Figure 6 is a view similar to Figure 5 with the plunger in its non-indicating position.

Figure 7 is a central, longitudinal, sectional view showing my invention incorporated with a fuse of the cartridge type.

Figure 8 is a central longitudinal section showing my invention incorporated with a plug adapted to be used between an appliance cord plug and a plug receptacle.

Figure 9 is an end elevation of the same showing the position of the indicator window between the prongs of the plug.

Figure 10 is a central, longitudinal, sectional view showing my invention incorporated directly in an appliance plug, with the conductor wires of the cord electrically connected in place.

Referring to the drawings in detail, wherein similar reference characters designate corresponding parts through the several views, the letter A generally indicates a fuse plug constructed in accordance with my invention, which includes a central body 55 formed of insulating material, which is adapted to be molded or cast around one end of the interior cartridge It.

The cartridge l6 forms one of the salient features of my invention, and the same includes an elongated cylindrical shell ll formed from steel, iron, or other electric conducting material which will not amalgamate with mercury.

The outer end of the cylinder E7 is snugly closed by a sight window I8, which can be formed from transparent material, such as mica, glass, etc. This sight window i8 is firmly held in place by a metallic ferrule is, so that the entrance and exit of air into the expansion chamber 26 of the cylinder I! will be substantially prevented.

The inner end of the cylinder is closed by an integral wall 2i arranged inward of the extreme inner end of the cylinder to define a chamber for the reception of the cylindrical plug 22 formed of insulating material, which is preferably fibre or a fibre compound of suitable composition to serve as an insulating part of the plug structure.

The opposite ends of the cylindrical plug have engaged therewith discs 23 and 2d preferably formed of copper or some material which has an aifinity for mercury. Engaged with the outer copper disc 24 is a central contact 25, which extends through the molded insulating body l5.

A metal ferrule 26 is employed for connecting the insulating plug 22, the copper disc 2d and the central contact 25 together.

The plug 22 is provided with an axially disposed capillary bore 21 which opens through an axial opening 28 in the inner copper disc 23 into a reservoir chamber 29 formed in the end wall 2| of the metallic cylinder ii. The reservoir chamber 29 communicates with the expansion chamber through a restricted outlet 39 formed in said end wall.

As shown, the metallic cylinder I! projects beyond the insulator body l5, and the outer end thereof carrying the sight'window i8 is received within an annular groove 3| formed about the sight opening 32 in the insulator shell 33 of the plug. This insulator'shell 33 is provided with a cylindrical skirt 3%, the inner end of which is snugly fitted on an annular shoulder 35 formed on the exterior of the insulator body IS. The insulator body l5 and the insulator shell 33 are connected and firmly joined together by the threaded metallic contact shell 35.

A fuse link 37 of a given amperage is electrically connected with the metallic cylinder H and with the metallic contact shell 36. As shown, this fuse link is extended through a notch 38 formed in the inner end of the insulator shell 33.

A quantity of electric conducting liquid, such as mercury, 39 is placed in the expansion chamber, and this mercury is adapted to fill the capillary bore 28 and the reservoir chamber 29, so as to bridge the contact discs 23 and 24. Preferably a slight excess of mercury is provided, as is clearly shown in the drawings, and the inner face of the wall 21 can be tapered or cone-shaped to receive the mercury, and the narrowed end of the tapered face communicates with the restricted outlet 31] of the reservoir chamber.

Also, in accordance with my invention, I slidably mount within the expansion chamber 20 of the metallic cylinder [1 an indicator plunger id which is preferably formed from heat resisting material. The outer face of the indicator plunger 40 carries suitable indicia, such as the word off, as indicated by the reference character 4|, for indicating a. blown fuse. Normally the plunger rests in the inner end of the chamber, so that the same cannot be readily seen through the sight window.

After the cartridge It has been sealed and the same has been incoporated in the fuse plug body, the fuse can be shaken so as to insure the position of the mercury column in the capillary bore and in the reservoir chamber. The fuse plug is now ready for use, and the same is threaded into its receptacle in a fuse block in the ordinary way. Should the circuit be shorted or subjected to an overload, the mercury column will blow into the expansion chamber, and the pressure will force the indicator plunger 40 to the outer end of the cylinder H, where the same can be readily seen by an observer.

After the fuse has blown, the circuit will be interrupted between the contacts 23 and 24. As the mercury is received into the expansion chamber 20, it will strike against the walls of the chamber and be cooled and condensed and formed into globules. These globules will pack in the lower end of the chamber, but will not flow into the reservoir chamber and the capillary bore.

The fuse can now be removed from its receptacle and forcibly shaken, which movement will force the mercury into the capillary bore and into the reservoir chamber. This movement will also return the indicator to its normal position at the inner end of the chamber.

The plunger 40 has a comparatively snug fit with the walls of the cylinder I1 so that the same will normally stay in a set position against movement due to the friction between the same and the walls of the chamber. However, the plunger is sufficiently loose to permit the forcible ejecting thereof from one end of the chamber and to permit the escape of air past the same.

The diameter and length of the capillary bore is carefully computed, as this controls the amperage of the fuse plug, and thus different diameters are provided for different sizes of plugs or plugs of different amperage.

If the bore 2'! becomes enlarged through repeated blowings of the fuse plug, then the fuse plug would carry a greater amperage than that for which it was designed. To overcome this contingency the safety fuse link 3? is provided. This safety fuse link 37 is of slightly greater amperage than the mercury column, and this fuse link will blow when this current value is reached. When the fuse link blows, the plug can be thrown away, if desired.

Particular stress is laid on the reservoir chamber 29, as this chamber forms means for maintaining the mercury column in place irrespectively of the position of the plug. The position of the mercury column is also maintained through the cohesion of the molecules of the mercury and the fact that the copper contact discs 23 and 2 3 have an afiinity for mercury.

In Figure 7 I have shown my invention incorporated with a fuse of the cartridge type, which is generally indicated by the reference character C. In this form of my invention the interior cartridge [6, previously described, is incorporated in an elongated cylindrical shell, or sleeve, 45, which is formed of insulating material. A rigid safety fuse link 46 is connected with one end of the cartridge and to a conductor disc 41, which is held in place on the shell d5 by means of the ferrule 48. The cartridge fuse functions in the same manner as the fuse plug described,

My invention is adapted to be incorporated with the cords of electrical appliances, and in Figure 8 I have shown a plug 50 which can be connected with the ordinary end plug of an appliance cord and with an outlet receptacle.

This plug 56 includes a body 5! formed of insulating material, closed at one end by a cap 52 also formed of insulating material. The cap 52 carries the contact prongs 53 and 54 which are adapted to engage the contacts of an outlet receptacle. The prong 53 has electrically connected therewith the resilient contact strip 55 which is adapted to be engaged by one prong of the plug of the appliance cord (not shown).

The other resilient contact strip 56 is electrically connected with one end contact of the interior cartridge 5? which is constructed the same as the cartridge IG heretofore described in detail. Ihe contact prong 54 is electrically connected with the cylindrical metallic shell of the interior fuse 51.

It is to be noted that the sight window for the cartridge appears through an opening 58 formed in the end cap 52 between the prongs 53 and 54.

In Figure 10 I have shown my invention incorporated directly with the end plug Gil of an electric appliance cord 6!. The plug 6!] includes an insulator body 52 closed at one end by an end cap 63 which carries the conductor prongs 64 and 65. These prongs are adapted to engage the resilient contacts of an outlet receptacle.

One prong G l is adapted to be electrically con nected with one conductor Wire 66 of the cord 6!, and the other prong 65 is electrically connected with the metallic cylindrical shell of my interior cartridge 67 which is also constructed the same as the interior cartridge it previously described.

[he other conductor wire 68 of the cord 6| is electrically connected with a conductor strip 69 which is in turn connected with the end contact of the interior cartridge. This strip 69 may be a fuse link, if so desired.

From the foregoing description, it can be seen that I have provided an exceptionally simple and durable renewable fuse having means for indicating the condition of said fuse.

Changes in details may be made without departing from the spirit or the scope of my invention, but What I claim as new is:

1. An electric fuse comprising a plug body of insulating material, shell and center contacts thereon, said body having a central bore consisting of a lower capillary portion and an upper larger portion constituting a relatively large expansion chamber, a body of mercury normally occupying said lower capillary portion and contacting with said center contact, and means for uniting the upper portion of the normal mercury column to said shell contact, said means including an apertured contact member through the aperture of which said mercury is adapted to extend whenever said mercury is in normal position in said lower capillary portion.

2. An electric fuse comprising a plug body of insulating material, shell and center contacts thereon, said body having a central bore consisting of a lower capillary portion and an upper larger portion constituting a relatively large expansion chamber, a body of mercury normally occupying said lower capillary portion and contacting with said center contact, means for uniting the upper portion of the normal mercury column to said shell contact, and a fuse link and other connections for electrically uniting the upper portion of the normal mercury column to said shell contact.

3. An electric fuse comprising a body, suitable external contacts on said body, said body having a capillary bore communicating with one of said contacts, conducting means leading from the other end of said bore to another of said contacts, and mercury normally located in said capillary bore and electrically uniting said contacts, said body having an expansion chamber communicating with said bore, into which chamber the mercury vapor is discharged from said capillary bore when the fuse is blown and in which chamber the mercury cools and forms globules which will not pass back into said bore sufiiciently to again complete the normal circuit until the mercury is agitated, as by shaking, said conducting means including a transversely apertured member through the aperture of which said mercury extends whenever the same is in normal circuit closing position in said capillary bore.

4. An electric fuse comprising a plug body of insulating material, shell, and center contacts thereon, said body having a central bore consisting of a lower capillary portion and an upper larger portion constituting a relatively large expansion chamber, a body of mercury normally occupying said lower capillary portion and contacting with said center contact, and means for uniting the upper portion of the normal mercury column to said shell contact, said means including in series connection a fuse link and an apertured contact member through the aperture of which said mercury is adapted to extend whenever said mercury is in normal position in said lower capillary portion.

5. An electric fuse comprising a body, suitable external contacts on said body, said body having a capillary bore communicating with one of said contacts, conducting means leading from the other end of said bore to another of said contacts, and mercury normally located in said capillary bore and electrically uniting said contacts, said body having an expansion chamber communicating with said bore, into which chamber the mercury vapor is discharged from said capillary bore when the fuse is blown and in which chamber the mercury cools and forms globules which will not pass back into said bore sufficiently to again complete the normal circuit until the mercury is agitated, as by shaking, said conducting means including in series connection a fuse link and a transversely apertured member through the aperture of which said mercury extends whenever the same is in normal circuit closing position in said capillary bore.

6. An electric fuse comprising, a plug body composed of insulating material, a peripheral shell contact on the outer surface of said body, a center contact carried by the body, a terminal in said body at a point'intermediate of its length, said body having a recess in its side in line with said intermediate terminal, a fuse link in said recess electrically connecting said intermediate terminal and said peripheral shell contact, and a body of mercury in a vertical capillary bore in said body, said mercury normally electrically connecting said center contact and intermediate terminal, the upper end of said capillary bore communicating with an expansion chamber at the outer end of said body.

'7. In an electric fuse, a fuse body having a side opening therein, said body having a capillary bore of a predetermined length and diameter, contacts at the opposite ends of said bore, mercury normally disposed in the capillary bore electrically connecting said contacts, the body having an expansion chamber communicating with the bore, a sight window closing the sight opening and the outer end of the expansion chamber, a slidable indicator mounted in said chamber adapted to be moved toward the sight window upon the blowing of the mercury from an overload, exterior contacts carried by the body, and means electrically connecting the exterior contacts and the first mentioned contacts.

8. An electric fuse comprising, a body of insulation, having a capillary bore therein, electric contacts arranged at the opposite ends of the bore, mercury normally positioned in said bore for electrically connecting said contacts, the body having an expansion chamber therein communicating with the bore, exterior contacts carried by the body electrically connected with the first mentioned contacts, a sight window normally closing the outer end of the expansion chamber, and an indicator plunger slidably mounted in the expansion chamber having indicia thereon and adapted to be forced toward the sight Window upon the blowing of the mercury by a current overload.

9. In an electric fuse, a fuse body formed of insulation, a cartridge fuse in said body including a metallic cylinder having an expansion chamber therein, a sight window closing the outer end of the expansion chamber and visible through one end of the body, a plug of insulating material carried by the body having a capillary bore communicating with the expansion chamber, contacts disposed at the opposite ends of the capillary bore, mercury normally disposed in the bore for electrically connecting said contacts, exterior contacts on the body electrically connected with the first mentioned contacts, and a plunger of heat resisting material slidably mounted in the expansion chamber movable toward the sight window upon the blowing of the mercury from an overload of current.

10. A renewable fuse comprising, a fuse cartridge including a metallic cylinder having an expansion chamber therein, and a reservoir chamber having a restricted outlet communicating with the expansion chamber, a plug of insulation carried by the cylinder having an axially disposed capillary bore communicating with the reservoir, a center contact connected with the plug, a quantity of mercury adapted to be normally disposed in the bore and the reservoir for electrically connecting the cylinder and the center contact, a body of insulation around the inner end of the cylinder, the plug of insulation and the center contact, a sight window carried by the outer end of the cylinder closing the expansion chamber, a cap of insulation receiving the body of insulation and the cylinder having a sight opening therein through which the sight window is visible, a conducting shell connecting the cap and body of insulation, a fuse link electrically connecting the shell with the cylinder, and a movable indicator in the expansion chamber adapted to be forced toward the sight window upon the blowing of mercury from an overload of electricity.

CHARLES J. McI-IUGH. 

